1. Field of the Invention
The invention relates to an apparatus for heating and degassing water by means of steam, essentially consisting of a column array accommodated in a housing and having a water feed line, leading above the column array into the housing, for the water which is to be heated and degassed, and having one steam feed line, leading into the housing, for the heating steam and one deaeration line for the gas/steam mixture which is to be extracted.
Such types of apparatus can be used in power station construction for degassing the condensate. In modern power station installations, particularly in combined types, the consumption of treated water is very high (15% and even more). The water consumed is replaced by cold make-up water which as a rule has a high air content. This leads to heavy heating and degassing duties.
Another important case is represented by the installations which produce process steam. The condensate flowing back from heat exchangers, reactors, heaters, etc., contains in most cases large quantities of dissolved air. In many cases, air-saturated make-up water (rain water) is also mixed in.
2. Discussion of Background
In connection with the degassing of liquids, exchange towers or columns are known, in which the steam and the liquid of a mixture are passed through in counter-current, in cross/counter-current or in co-current relative to one another (LUEGER, volume 16, Lexikon der Verfahrenstechnik [Dictionary of process engineering], 4th edition, Deutsche Verlags-Anstalt Stuttgart, page 51). In these columns, the liquid and the vapor of a mixture to be separated are passed through in counter-current or in co-current relative to one another in such a way that the two phases come into the most intimate contact possible for mass transfer and heat exchange.
The use of a degassing column in counter-current arrangement is correct in principle for obtaining the greatest separation effect at a defined column height. Major condensate streams at significant subcooling, however, involve the problem, in the case of a counter-current arrangement, that a very large proportion of the steam must overcome the lower part of the column (flooding of the packing due to higher steam loading), without a significant effect on the mass-kinetic separation effect, which arises in the lower part of the column, since the heating and the saturation process of the condensate take place in the upper part. The consequence of such a design solution is, however, that the diameter of the column must be increased enormously, in order to prevent flooding of the packing, with considerable additional costs for the apparatus.
At a high heating duty and a low required degassing effect, degassers with co-current arrangement can be used. The advantage of this arrangement is that the required large steam flow is introduced directly at the top in the mixing chamber, where the condensate is heated up. In addition to the preheated condensate, the flushing steam flows through the co-current column. This arrangement thus allows extensive heating of the condensate without a risk of flooding. The disadvantage of the co-current arrangement is that a high degassing effect cannot be achieved.